Silver halide monocrystal particle-tract detectors doped with manganese

ABSTRACT

The photographic properties in particular the light sensitivity of silver halide monocrystal-track detectors are highly improved by adding manganese ions as doping agents.

United States Patent 91 1 3,718,606 Haase et al. 1 Feb. 27, 1973 1SILVER HALIDE MONOCRYSTAL 1 References Cited PARTICLE-TRACT DETECTORSDOPED WITH MANGANESE UNITED STATES PATENTS [75] Inventors. Gunter Ham,Frankfurt am Mal-n; 3,362,797 1/1968 Shaskolskaja ..252 1 Erwinschopper, Koenigstein/Tau 3,548,191 12/1970 Schultz ..252/408 nus, bothof Germany [73] Assignee: Agfa-Gevaert Aktiengesellscllaft,

Leverkusen, Germany Primary Examiner-John T. Goolkasian [22] Flled' 1970Assistant Examiner-M. E. McCamish [21] Appl. No.: 86,277Attorney-Connolly and Hutz [30] Foreign Application Priority Data 1 ..Pl 8 42 .9 Nov 21 969 Germany 9 5 5 ABSTRACT US. Cl. t t R, Thephotographic properties in particular the [5 Into u G011 ensitivity ofilver monocrystal tra k d t ctor [58] Field of Search ..252/408, 1;250/83 R, 83.1;

23/300, 304, 295, 87 R, 91, 205, 204 R, 367; 96/50 R, 94 R, 94 BF, 120,110,119 R; 148/].6

are highly improved by adding manganese ions as doping agents.

4 Claims, No Drawings SILVER HALIDE MONOCRYSTAL PARTICLE- TRACTDETECTORS DOPED WITH MANGANESE This invention relates to particle-trackdetectors based on silver halide monocrystals whose sensitivity andfogging are improved by the addition of specific doping agents.

Solid state particle'track detectors for detecting tracks of ionizingparticles are being used to an increasing extent in the investigation ofatomic particles in nuclear physics, above all in the physics of cosmicradiation and in modern heavy-ion physics. In cases where they areintended to be used for quantitative measurements, particle-trackdetectors of this kind have to meet certain requirements, moreparticular the particle track must be developed in a clearlyreproduciblemanner which is characteristic of the interaction of the particle to beinvestigated with the solid.

The particle track has to provide as much information as possible on theparticle. It should also lend itself to quick and easy evaluation.

Since the defects which an ionizing particle produces in a solid aresubmicroscopic in their dimensions, a mechanism by which the track canbe amplified should be available for photooptical evaluation, forexample for rendering the track visible. The defects produced by theionizing particle in the solid represent the latent image of theparticle track which is developed by the amplifying mechanism. The moredetails characteristic of the particle the amplified particle trackdiscloses, the more effective the detector will be.

Two amplifying mechanisms have acquired practical significance:

l. Selective etching of the solid along the particle track.

2. The deposition of a new phase along the track.

Etching has acquired significance inter alia in the case of mica and afew glasses, especially organic glasses. The process of selectiveetching along the particle track is essentially based upon the fact thatbonds broken along the track make the etching process much easier.Unfortunately, etching involves several difficulties which seriouslyrestrict the utility of this technique.

The most serious disadvantage of the etching process is that valuabledetails are often lost, above all in the case of long particle tracks,because the etching medium has to penetrate through the solid fromoutside along the track and the etching channels available for thispurpose are extremely narrow with the result that in many cases theetchingmedium is unable to penetrate sufficiently deeply into the soliddetector. For this reason, it is not generally possible to amplifyinterrupted particle tracks.

It is also known that the tracks left by ionizing particles can bedetected in silver chloride monocrystals. In this type of detector, anew phase is preferably deposited along the particle track. In the caseof silver halide monocrystals, this new phase consists essentially ofsilver.

The silver chloride monocrystals are superior to the aforementionedsolid state particle-track detectors in which the particle tracks haveto be amplified by an etching process, in particular by virtue of thefact that, in the case of silver chloride monocrystals, the amplifyingand developing process can be carried out very quickly and easily. Inthe amplifying process, the

monocrystal in which the particle track was recorded is uniformlyexposed with high-energy light, preferably ultra-violet light.

The developing process can be explained as follows: Electron-defectelectron pairs are produced in the crystal through the exposure tolight. The electrons are trapped along the particle track in interchangewith silver ions from the disturbed regions. The track is thusstabilized and then amplified. In principle, this process is comparablewith the elementary photographic process. The original track is thelatent image of the track, so that amplification corresponds tophotographic development.

The disadvantage of these silver chloride monocrystal detectorsoriginally lay in their inadequate reproducibility. This disadvantagewas obviated by using high-purity silver chloride for producing thedetectors. It is known of high-purity silver chloride that it isbasically non-sensitive and unsuitable for the production of detectors.However, silver chloride monocrystals of this kind can be sensitized forionizing particles by the addition to them of small quantities ofcertain foreign substances, such as cadmium or lead for example.Reference is made in this connection to the article by K. Breuer, G.I-Iaase and E. Schopper in Brit. J. Appl. Phys, 18 (1967), 1824 et seq.and the article by K. Breuer, E. Schopper, G. Haase and F. Zorgiebel inPhot. Korrespondenz 104 (I968) 76 et seq. The silver chloride crystalsdoped in the manner described show a level of sensitivity to ionizingparticles which is adequate for many purposes. They are alsoadvantageous insofar as they do not record gamma-rays, X-rays andelectrons so that no disturbing background is produced by these rays.

Unfortunately, silver chloride monocrystals doped solely with cadmiumdid not satisfy practical requirements for more accurate quantitativemeasurements on tracks left by ionizing particles, either in regard tosensitivity or, more particularly in regard to the background, i.e., thesignal-noise ratio. The background adversely affecting evaluation of theparticle tracks is essentially attributable to l. the lattice defectswhich are present in the crystal,

i.e., before particle irradiation, and which can never be completelyeliminated, especially distortion of narrow-angle grain boundaries ofgeneral sub-structures which, like the lattice defects produced byparticle irradiation, are decorated with silver along the tracks duringthe amplifying process; 2. Silver particles produced by photolysisduring amplification, being statistically distributed We now have foundsilver halide monocrystal detectors for recording tracks of ionizingparticles which contain manganese ions as doping agents.

The addition of manganese considerably increases the sensitivity of thecrystals and the information content of particle tracks and largelyeliminates the background interfering with the evaluation of theparticle tracks. More particularly, the optical crystal haze caused bydeposits in the silver halide monocrystal detectors doped with cadmiumis completely avoided. The particle tracks in the silver halidemonocrystal detectors doped with manganese are extremely finegrained andare visible in every detail on an optically substantially clearbackground, being particularly suitable for accurate quantitativemeasurements.

The concentration of the manganese ions can vary within wide limits. Ingeneral, concentrations of from 100 ppm to 3,000 ppm of manganese ions,based on the weight of the silver halide, preferably silver chloride,have proved to be sufficient. Additions of from 500 to 1,500 ppm arepreferred.

The ions of tetravalent manganese are particularly effective. In thiscase, doping can readily be achieved for example by the addition ofmanganese (II) salt solutions to the silver halide, followed by meltingin a chlorine atmosphere. The silver halide monocrystals doped withmanganese are then grown in a chlorinecontaining atmosphere. Atrelatively high chlorine partial pressures, gas bubbles can be formed inthe silver halide monocrystals doped with manganese. Formation of gasbubbles can be avoided forexample by reducing the chlorine partialpressure, by adding an inert gas, for example nitrogen and by reducingthe rate at which the monocrystals are grown. For example, a gasatmosphere which had a total pressure of 400 Torr and which containedchlorine with a partial pressure of 5 Torr and nitrogen with a partialpressure of 395 Torr, has proved to be favorable.

The particle-track detectors according to the invention can be used fordetermining particle data, for investigating particle reactions andnuclear fission and for investigating decay mechanisms even ofextraheavy nuclei, for identifying isotopes of high-energy ions and forinvestigating isotope compositions of solar radiation or cosmicradiation and for determining the sources of this radiation. Thesedetectors are particularly suitable for recording the tracks of heavyions.

The tracks of ionizing particles can be amplified in the usual way inthe detectors according to the invention by uniform exposure toshort-wave light, especially ultra-violet light. Thus, very distinctlydeveloped tracks can be obtained on a clear background. In this respect,the detectors are superior to conventional photographic emulsions forrecording nuclear tracks nuclear track emulsions"). These materialsconsist of a supported silver halide gelatin emulsion layer of highresolving power. In general, it is not possible to obtain in thesephotographic emulsions particle tracks as sharp as those in thedetectors according to the invention. In addition, the photographicemulsions usually have a much greater disturbing background because theyare also sensitive to gamma-rays, X-rays and electrons.

In the detectors according to the invention, the tracks of ionizingparticles can be amplified substantially over any part of their entirelength, even in cases where they are interrupted, i.e., where relativelyfew or undisturbed crystal regions in which the track is interrupted aresituated between the more strongly disturbed crystal regions produced bythe ionizing tracks passing through. This automatically follows from thenature of the amplifying process since, during the amplifying processwhich takes place inside the volume, electrons and silver ions aredeposited wherever lattice defects have been produced by the ionizingparticles passing through. In this respect, the detectors according tothe invention are generally superior to detectors of the kind in whichthe track is amplified by etching. The etching process begins at thesurface of the detector where the ionizing particle has entered thecrystal and continues along the track of the particle into the interiorof the crystal so that fresh etching solution has to be supplied alongthe channel already formed by the etching process. With interruptedparticle tracks, the etching process is liable to stop at the end of atrack section because the etching solution cannot then penetratesufficiently quickly into the adjacent undisturbed region of thecrystal, so that the following sections of track which are notcontinuous with the previous track can no longer be amplified. In somecases, in the case of interrupted particle tracks, a less disturbed oreven undisturbed crystal region between two track sections may bepenetrated by the etching solution if the time allowed for the etchingsolution to act is considerably increased. In that case, however, theetching solution also continues to act during this period in thatportion of the track which was etched first and which has therefore beenamplified, with the result that this first section of track becomesgreatly increased in width and may acquire a pronounced cone shape.However, this seriously impairs the reproducibility of the track and theaccuracy of evaluation. The detectors according to the invention arecompletely free from such disadvantages.

The possibility provided by the silver halide monocrystal detectorsaccording to the invention of amplifying, with uniform distinction andhigh reproducibility, even those particle tracks which start at somedepth within the detector, opens up fields of application for thesedetectors in which other solid state particle-track detectors ofhitherto known type could not be used with the same assurance andaccuracy. An example of this is the study of the run-down of decayprocesses as a function of time. If the particle tracks are amplified ata first point in time t and then at a point in time 2,, it is possibleto determine which tracks have been added during the time intervalt,--t,,, i.e., which new decay processes have occurred inside thedetector during the time interval t,r,,.

In many cases, uniform exposure with the short-wave light producing theelectron-defect electron pairs is sufficient in detectors according tothe invention for amplifying the particle tracks. However, this methodof amplification can easily be improved in the detectors according tothe invention in order to amplify particle tracks situated at almost anydepth inside the crystal. This was not possible with conventional solidstate particle-track detectors.

In the case of relatively thick crystals and tracks situated deep insidethe crystal, the electrons required for the amplification process can bemade to penetrate sufficiently deeply into the interior of the crystalby exposing the crystal impulse-fashion to the short-wave lightproducing the electron defect electron pairs, whilst asynchronouslypulsed electrical field is applied to the crystal so that, for theduration of each of the shortterm exposure impulses, there is effectivein the crystal an equally brief electrical field which causes theelectrons produced by the exposure impulse, and only these electrons, todrift through the crystal volume. This method of combining pulsedexposure with pulsed electrical fields is generally known in the physicsof solids, for example for determining the lives and ranges of electronsin the solid (cf. the references in the aforementioned works).Short-lived electrical field impulses are used in this method of trackamplification in silver halide monocrystal detectors because they avoidthe troublesome movement of silver ions which would occur in longerlasting electrical fields.

In the case of relatively thick crystals and tracks situated deep insidethe crystal, the advantage of the weak background and the absence ofcrystal haze in the detectors according to the invention as comparedwith detectors of silver halide doped solely with cadmium, isparticularly noticeable. In the case of detectors with a relativelystrong background or relatively pronounced crystal haze, for example inthe case of crystals doped with cadmium in high concentrations, deeplying tracks could not be evaluated at all, or with far from therequired degree of accuracy.

Both embodiments of the amplification process used in the detectorsaccording to the invention, i.e., solely by uniformly exposing thedetectors to short-wave light or by pulsed exposure with short-wavelight in a synchronously pulsed electrical field, are characterized intheir simplicity and stability to interference. After the particle trackhas been recorded, the detectors are not exposed to any liquids so thatany disturbances which might be caused by liquids are avoided. lt isworth mentioning here the sensitivity of the etching methods in thisrespect and the swelling and distortion phenomena which occur in theconventional photographic processing of nuclear track emulsions.

EXAMPLE An aqueous solution of manganese (ID-chloride (p.a.) is addedthrough a pipette to 99.999 percent pure silver chloride in powder formin such a way that a silver chloride containing 1,000 ppm of manganeseis obtained. The mixture is dried in the pipette in a drying chamber.The silver chloride doped with manganese is then fused in the pipette.The melt is introduced between two quartz glass plates heated to about550 C. the gap between which is set at about 200 p. by small rods ofquartz glass. On cooling, a polycrystalline manganese-doped silverchloride wafer is obtained. The sandwich consisting of the two quartzglass plates and the silver chloride wafer between them is introducedinto a horizontal quartz glass tube which, following evacuation, isfilled with a gas mixture with a total pressure of 400 Torr consistingof chlorine with a partial pressure of 5 Torr and nitrogen with apartial pressure of 395 Torr. Thereafter, a tubular oven is passed overthe quartz glass tube with such a temperature gradient and at such a seed that the polycrystalline rnan anesedoped silver c loride wafer 15converted in a nown manner through fusion into a monocrystal which canbe detached from the quartz plates by immersing the sandwich in water.

Following irradiation with the ionizing particles to be investigatedwhose tracks are to be recorded, the silver chloride monocrystal dopedwith manganese is uniformly exposed to a high-pressure xenon lamp with afilter between the light source and the detector so that only a narrowwave length range around 417 nm is effective. The intensity of theshort-wave light directed on to the monocrystal amounts to about 10quanta/cm sec. The exposure time is about 20 to 30 minutes.

We claim:

1. A silver halide monocrystal detector for recording the tracks. ofionizing particles containing a doping agent, said doping agentcontaining manganese ions.

2. A detector as defined in claim 1, containing manganese ions inquantities of from 500 ppm to 1,500 PP 3. A detector as defined in claim1, containing ions of tetravalent manganese.

4. A detector as defined in claim 1, wherein the silver halide is silverchloride.

2. A detector as defined in claim 1, containing manganese ions in quantities of from 500 ppm to 1,500 ppm.
 3. A detector as defined in claim 1, containing ions of tetravalent manganese.
 4. A detector as defined in claim 1, wherein the silver halide is silver chloride. 